机械自动化 外文翻译 外文文献 英文文献 刀具和刀夹.doc

CUTTING TOOLS AND TOOLHOLDERS To machine a workpiece successfully you must have : the correct kind of cutting tool or tool bit the right type of toolholder a tool with a sharp cutting-edge the cutting tool set or adjusted to the correct height and position. Cutting-tool materials Tool bits used on the lathe are made form one of six basic materials: water-hardening steels,high-speed steels,hard-cast,nonferrous alloys,sintered (cemented) carbides,ceramics,and diamonds. The selection of the material used depends upon many factors including:tool cost,size and design of tool ,metal-removal rate ,length of run ,finish and tolerance of part,and condition and capability of the machine tool . Because of these factors ,material selection is more often based on general experience than on precise evaluation . There are, however ,certain general characteristics of the different cutting-tool materials you should understand. Water-hardening Steels.These include the high-carbon tool steels (either plain carbon or those with minor additions of chromium , vanadium,or tungsten) .The different grades of water-hardening tool steels are classed as W steels in American Iron and Steel Institute’s system of classification . Tools made from these materials have very sharp ,smooth cutting-edges when properly heat-treated. They are adequate for limited turning at a relatively low cutting speed or when old ,low-speed equipment ,such as a flat-belt lathe , is used . The main limitation of tools made form water-hardening steels is that they soften if the cutting-edge temperature exceeds approximately 300-400F during sharpening or cutting .A second disadvantage is low resistance to edge wear . High-speed Steels. High-speed steels offer great improvement in cutting efficiency over water-hardening tool steels .Tools made from high-speed steels retain enough hardness to machine at rapid rates even when the tool temperature reaches 1050F . They can be used even though they become dull red with heat